Variability of bed drag on cohesive beds under wave action
MetadataShow full item record
KeywordWater waves; Muddy waters; Coastal waters; Currents; Bed drag; Drag coefficient; Bottom shear stress; Bottom friction; Mud; Cohesive sediment
Drag force at the bed acting on water flow is a major control on water circulation and sediment transport. Bed drag has been thoroughly studied in sandy waters, but less so in muddy coastal waters. The variation of bed drag on a muddy shelf is investigated here using field observations of currents, waves, and sediment concentration collected during moderate wind and wave events. To estimate bottom shear stress and the bed drag coefficient, an indirect empirical method of logarithmic fitting to current velocity profiles (log-law), a bottom boundary layer model for combined wave-current flow, and a direct method that uses turbulent fluctuations of velocity are used. The overestimation by the log-law is significantly reduced by taking turbulence suppression due to sediment-induced stratification into account. The best agreement between the model and the direct estimates is obtained by using a hydraulic roughness of 10 m in the model. Direct estimate of bed drag on the muddy bed is found to have a decreasing trend with increasing current speed, and is estimated to be around 0.0025 in conditions where wave-induced flow is relatively weak. Bed drag shows an increase (up to fourfold) with increasing wave energy. These findings can be used to test the bed drag parameterizations in hydrodynamic and sediment transport models and the skills of these models in predicting flows in muddy environments.
© The Author(s), 2016. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Water 8 (2016): 131, doi:10.3390/w8040131.
The following license files are associated with this item:
Showing items related by title, author, creator and subject.
Precession-driven changes in Iceland–Scotland Overflow Water penetration and bottom water circulation on Gardar Drift since ~ 200 ka Elmore, Aurora C.; Wright, James D.; Chalk, Thomas B. (2015-09-21)Benthic foraminiferal stable isotopic records from a transect of sediment cores south of the Iceland-Scotland Ridge reveal that the penetration depth of Iceland-Scotland Overflow Water (ISOW) varied on orbital timescales ...
Morford, Jennifer L.; Martin, William R.; Carney, Caitlin M. (2009-01-23)We measured U in sediments (both pore waters and solid phase) from three locations on the middle Atlantic Bight (MAB) from the eastern margin of the United States: a northern location on the continental shelf off ...
Trans-equatorial bottom water flow in the western Atlantic : volume XLVI in a series of reports presenting data from moored current meters Tarbell, Susan A.; Whitehead, John A.; Hall, Melinda M.; McCartney, Michael S. (Woods Hole Oceanographic Institution, 1997-02)Current and temperature measurements from Vector Averaging Current Meters (VACMs) deployed from September 1992 to June 1994 as part of the Deep Basin Experiment (DBE) measuring the trans-equatorial water flow are presented. ...